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<body>
<div class="document" id="numpy-i-a-swig-interface-file-for-numpy">
<h1 class="title">numpy.i: a SWIG Interface File for NumPy</h1>
<table class="docinfo" frame="void" rules="none">
<col class="docinfo-name" />
<col class="docinfo-content" />
<tbody valign="top">
<tr><th class="docinfo-name">Author:</th>
<td>Bill Spotz</td></tr>
<tr class="field"><th class="docinfo-name">Institution:</th><td class="field-body">Sandia National Laboratories</td>
</tr>
<tr><th class="docinfo-name">Date:</th>
<td>1 December, 2007</td></tr>
</tbody>
</table>
<div class="contents topic">
<p class="topic-title first"><a id="contents" name="contents">Contents</a></p>
<ul class="simple">
<li><a class="reference" href="#introduction" id="id1" name="id1">Introduction</a></li>
<li><a class="reference" href="#using-numpy-i" id="id2" name="id2">Using numpy.i</a></li>
<li><a class="reference" href="#available-typemaps" id="id3" name="id3">Available Typemaps</a><ul>
<li><a class="reference" href="#input-arrays" id="id4" name="id4">Input Arrays</a></li>
<li><a class="reference" href="#in-place-arrays" id="id5" name="id5">In-Place Arrays</a></li>
<li><a class="reference" href="#argout-arrays" id="id6" name="id6">Argout Arrays</a></li>
<li><a class="reference" href="#argoutview-arrays" id="id7" name="id7">Argoutview Arrays</a></li>
<li><a class="reference" href="#output-arrays" id="id8" name="id8">Output Arrays</a></li>
<li><a class="reference" href="#other-common-types-bool" id="id9" name="id9">Other Common Types: bool</a></li>
<li><a class="reference" href="#other-common-types-complex" id="id10" name="id10">Other Common Types: complex</a></li>
</ul>
</li>
<li><a class="reference" href="#numpy-array-scalars-and-swig" id="id11" name="id11">NumPy Array Scalars and SWIG</a><ul>
<li><a class="reference" href="#why-is-there-a-second-file" id="id12" name="id12">Why is There a Second File?</a></li>
</ul>
</li>
<li><a class="reference" href="#helper-functions" id="id13" name="id13">Helper Functions</a><ul>
<li><a class="reference" href="#macros" id="id14" name="id14">Macros</a></li>
<li><a class="reference" href="#routines" id="id15" name="id15">Routines</a></li>
</ul>
</li>
<li><a class="reference" href="#beyond-the-provided-typemaps" id="id16" name="id16">Beyond the Provided Typemaps</a><ul>
<li><a class="reference" href="#a-common-example" id="id17" name="id17">A Common Example</a></li>
<li><a class="reference" href="#other-situations" id="id18" name="id18">Other Situations</a></li>
<li><a class="reference" href="#a-final-note" id="id19" name="id19">A Final Note</a></li>
</ul>
</li>
<li><a class="reference" href="#summary" id="id20" name="id20">Summary</a></li>
<li><a class="reference" href="#acknowledgements" id="id21" name="id21">Acknowledgements</a></li>
</ul>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id1" id="introduction" name="introduction">Introduction</a></h1>
<p>The Simple Wrapper and Interface Generator (or <a class="reference" href="http://www.swig.org">SWIG</a>) is a powerful tool for generating wrapper
code for interfacing to a wide variety of scripting languages.
<a class="reference" href="http://www.swig.org">SWIG</a> can parse header files, and using only the code prototypes,
create an interface to the target language.  But <a class="reference" href="http://www.swig.org">SWIG</a> is not
omnipotent.  For example, it cannot know from the prototype:</p>
<pre class="literal-block">
double rms(double* seq, int n);
</pre>
<p>what exactly <tt class="docutils literal"><span class="pre">seq</span></tt> is.  Is it a single value to be altered in-place?
Is it an array, and if so what is its length?  Is it input-only?
Output-only?  Input-output?  <a class="reference" href="http://www.swig.org">SWIG</a> cannot determine these details,
and does not attempt to do so.</p>
<p>If we designed <tt class="docutils literal"><span class="pre">rms</span></tt>, we probably made it a routine that takes an
input-only array of length <tt class="docutils literal"><span class="pre">n</span></tt> of <tt class="docutils literal"><span class="pre">double</span></tt> values called <tt class="docutils literal"><span class="pre">seq</span></tt>
and returns the root mean square.  The default behavior of <a class="reference" href="http://www.swig.org">SWIG</a>,
however, will be to create a wrapper function that compiles, but is
nearly impossible to use from the scripting language in the way the C
routine was intended.</p>
<p>For <a class="reference" href="http://www.python.org">python</a>, the preferred way of handling
contiguous (or technically, <em>strided</em>) blocks of homogeneous data is
with the module <a class="reference" href="http://numpy.scipy.org">NumPy</a>, which provides full
object-oriented access to multidimensial arrays of data.  Therefore,
the most logical <a class="reference" href="http://www.python.org">python</a> interface for the <tt class="docutils literal"><span class="pre">rms</span></tt> function would be
(including doc string):</p>
<pre class="literal-block">
def rms(seq):
    &quot;&quot;&quot;
    rms: return the root mean square of a sequence
    rms(numpy.ndarray) -&gt; double
    rms(list) -&gt; double
    rms(tuple) -&gt; double
    &quot;&quot;&quot;
</pre>
<p>where <tt class="docutils literal"><span class="pre">seq</span></tt> would be a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array of <tt class="docutils literal"><span class="pre">double</span></tt> values, and its
length <tt class="docutils literal"><span class="pre">n</span></tt> would be extracted from <tt class="docutils literal"><span class="pre">seq</span></tt> internally before being
passed to the C routine.  Even better, since <a class="reference" href="http://numpy.scipy.org">NumPy</a> supports
construction of arrays from arbitrary <a class="reference" href="http://www.python.org">python</a> sequences, <tt class="docutils literal"><span class="pre">seq</span></tt>
itself could be a nearly arbitrary sequence (so long as each element
can be converted to a <tt class="docutils literal"><span class="pre">double</span></tt>) and the wrapper code would
internally convert it to a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array before extracting its data
and length.</p>
<p><a class="reference" href="http://www.swig.org">SWIG</a> allows these types of conversions to be defined via a
mechanism called typemaps.  This document provides information on how
to use <tt class="docutils literal"><span class="pre">numpy.i</span></tt>, a <a class="reference" href="http://www.swig.org">SWIG</a> interface file that defines a series of
typemaps intended to make the type of array-related conversions
described above relatively simple to implement.  For example, suppose
that the <tt class="docutils literal"><span class="pre">rms</span></tt> function prototype defined above was in a header file
named <tt class="docutils literal"><span class="pre">rms.h</span></tt>.  To obtain the <a class="reference" href="http://www.python.org">python</a> interface discussed above,
your <a class="reference" href="http://www.swig.org">SWIG</a> interface file would need the following:</p>
<pre class="literal-block">
%{
#define SWIG_FILE_WITH_INIT
#include &quot;rms.h&quot;
%}

%include &quot;numpy.i&quot;

%init %{
import_array();
%}

%apply (double* IN_ARRAY1, int DIM1) {(double* seq, int n)};
%include &quot;rms.h&quot;
</pre>
<p>Typemaps are keyed off a list of one or more function arguments,
either by type or by type and name.  We will refer to such lists as
<em>signatures</em>.  One of the many typemaps defined by <tt class="docutils literal"><span class="pre">numpy.i</span></tt> is used
above and has the signature <tt class="docutils literal"><span class="pre">(double*</span> <span class="pre">IN_ARRAY1,</span> <span class="pre">int</span> <span class="pre">DIM1)</span></tt>.  The
argument names are intended to suggest that the <tt class="docutils literal"><span class="pre">double*</span></tt> argument
is an input array of one dimension and that the <tt class="docutils literal"><span class="pre">int</span></tt> represents
that dimension.  This is precisely the pattern in the <tt class="docutils literal"><span class="pre">rms</span></tt>
prototype.</p>
<p>Most likely, no actual prototypes to be wrapped will have the argument
names <tt class="docutils literal"><span class="pre">IN_ARRAY1</span></tt> and <tt class="docutils literal"><span class="pre">DIM1</span></tt>.  We use the <tt class="docutils literal"><span class="pre">%apply</span></tt> directive to
apply the typemap for one-dimensional input arrays of type <tt class="docutils literal"><span class="pre">double</span></tt>
to the actual prototype used by <tt class="docutils literal"><span class="pre">rms</span></tt>.  Using <tt class="docutils literal"><span class="pre">numpy.i</span></tt>
effectively, therefore, requires knowing what typemaps are available
and what they do.</p>
<p>A <a class="reference" href="http://www.swig.org">SWIG</a> interface file that includes the <a class="reference" href="http://www.swig.org">SWIG</a> directives given
above will produce wrapper code that looks something like:</p>
<pre class="literal-block">
 1 PyObject *_wrap_rms(PyObject *args) {
 2   PyObject *resultobj = 0;
 3   double *arg1 = (double *) 0 ;
 4   int arg2 ;
 5   double result;
 6   PyArrayObject *array1 = NULL ;
 7   int is_new_object1 = 0 ;
 8   PyObject * obj0 = 0 ;
 9
10   if (!PyArg_ParseTuple(args,(char *)&quot;O:rms&quot;,&amp;obj0)) SWIG_fail;
11   {
12     array1 = obj_to_array_contiguous_allow_conversion(
13                  obj0, NPY_DOUBLE, &amp;is_new_object1);
14     npy_intp size[1] = {
15       -1
16     };
17     if (!array1 || !require_dimensions(array1, 1) ||
18         !require_size(array1, size, 1)) SWIG_fail;
19     arg1 = (double*) array1-&gt;data;
20     arg2 = (int) array1-&gt;dimensions[0];
21   }
22   result = (double)rms(arg1,arg2);
23   resultobj = SWIG_From_double((double)(result));
24   {
25     if (is_new_object1 &amp;&amp; array1) Py_DECREF(array1);
26   }
27   return resultobj;
28 fail:
29   {
30     if (is_new_object1 &amp;&amp; array1) Py_DECREF(array1);
31   }
32   return NULL;
33 }
</pre>
<p>The typemaps from <tt class="docutils literal"><span class="pre">numpy.i</span></tt> are responsible for the following lines
of code: 12--20, 25 and 30.  Line 10 parses the input to the <tt class="docutils literal"><span class="pre">rms</span></tt>
function.  From the format string <tt class="docutils literal"><span class="pre">&quot;O:rms&quot;</span></tt>, we can see that the
argument list is expected to be a single <a class="reference" href="http://www.python.org">python</a> object (specified
by the <tt class="docutils literal"><span class="pre">O</span></tt> before the colon) and whose pointer is stored in
<tt class="docutils literal"><span class="pre">obj0</span></tt>.  A number of functions, supplied by <tt class="docutils literal"><span class="pre">numpy.i</span></tt>, are called
to make and check the (possible) conversion from a generic <a class="reference" href="http://www.python.org">python</a>
object to a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.  These functions are explained in the
section <a class="reference" href="#helper-functions">Helper Functions</a>, but hopefully their names are
self-explanatory.  At line 12 we use <tt class="docutils literal"><span class="pre">obj0</span></tt> to construct a <a class="reference" href="http://numpy.scipy.org">NumPy</a>
array.  At line 17, we check the validity of the result: that it is
non-null and that it has a single dimension of arbitrary length.  Once
these states are verified, we extract the data buffer and length in
lines 19 and 20 so that we can call the underlying C function at line
22.  Line 25 performs memory management for the case where we have
created a new array that is no longer needed.</p>
<p>This code has a significant amount of error handling.  Note the
<tt class="docutils literal"><span class="pre">SWIG_fail</span></tt> is a macro for <tt class="docutils literal"><span class="pre">goto</span> <span class="pre">fail</span></tt>, refering to the label at
line 28.  If the user provides the wrong number of arguments, this
will be caught at line 10.  If construction of the <a class="reference" href="http://numpy.scipy.org">NumPy</a> array
fails or produces an array with the wrong number of dimensions, these
errors are caught at line 17.  And finally, if an error is detected,
memory is still managed correctly at line 30.</p>
<p>Note that if the C function signature was in a different order:</p>
<pre class="literal-block">
double rms(int n, double* seq);
</pre>
<p>that <a class="reference" href="http://www.swig.org">SWIG</a> would not match the typemap signature given above with
the argument list for <tt class="docutils literal"><span class="pre">rms</span></tt>.  Fortunately, <tt class="docutils literal"><span class="pre">numpy.i</span></tt> has a set of
typemaps with the data pointer given last:</p>
<pre class="literal-block">
%apply (int DIM1, double* IN_ARRAY1) {(int n, double* seq)};
</pre>
<p>This simply has the effect of switching the definitions of <tt class="docutils literal"><span class="pre">arg1</span></tt>
and <tt class="docutils literal"><span class="pre">arg2</span></tt> in lines 3 and 4 of the generated code above, and their
assignments in lines 19 and 20.</p>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id2" id="using-numpy-i" name="using-numpy-i">Using numpy.i</a></h1>
<p>The <tt class="docutils literal"><span class="pre">numpy.i</span></tt> file is currently located in the <tt class="docutils literal"><span class="pre">numpy/docs/swig</span></tt>
sub-directory under the <tt class="docutils literal"><span class="pre">numpy</span></tt> installation directory.  Typically,
you will want to copy it to the directory where you are developing
your wrappers.  If it is ever adopted by <a class="reference" href="http://www.swig.org">SWIG</a> developers, then it
will be installed in a standard place where <a class="reference" href="http://www.swig.org">SWIG</a> can find it.</p>
<p>A simple module that only uses a single <a class="reference" href="http://www.swig.org">SWIG</a> interface file should
include the following:</p>
<pre class="literal-block">
%{
#define SWIG_FILE_WITH_INIT
%}
%include &quot;numpy.i&quot;
%init %{
import_array();
%}
</pre>
<p>Within a compiled <a class="reference" href="http://www.python.org">python</a> module, <tt class="docutils literal"><span class="pre">import_array()</span></tt> should only get
called once.  This could be in a C/C++ file that you have written and
is linked to the module.  If this is the case, then none of your
interface files should <tt class="docutils literal"><span class="pre">#define</span> <span class="pre">SWIG_FILE_WITH_INIT</span></tt> or call
<tt class="docutils literal"><span class="pre">import_array()</span></tt>.  Or, this initialization call could be in a
wrapper file generated by <a class="reference" href="http://www.swig.org">SWIG</a> from an interface file that has the
<tt class="docutils literal"><span class="pre">%init</span></tt> block as above.  If this is the case, and you have more than
one <a class="reference" href="http://www.swig.org">SWIG</a> interface file, then only one interface file should
<tt class="docutils literal"><span class="pre">#define</span> <span class="pre">SWIG_FILE_WITH_INIT</span></tt> and call <tt class="docutils literal"><span class="pre">import_array()</span></tt>.</p>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id3" id="available-typemaps" name="available-typemaps">Available Typemaps</a></h1>
<p>The typemap directives provided by <tt class="docutils literal"><span class="pre">numpy.i</span></tt> for arrays of different
data types, say <tt class="docutils literal"><span class="pre">double</span></tt> and <tt class="docutils literal"><span class="pre">int</span></tt>, and dimensions of different
types, say <tt class="docutils literal"><span class="pre">int</span></tt> or <tt class="docutils literal"><span class="pre">long</span></tt>, are identical to one another except
for the C and <a class="reference" href="http://numpy.scipy.org">NumPy</a> type specifications.  The typemaps are
therefore implemented (typically behind the scenes) via a macro:</p>
<pre class="literal-block">
%numpy_typemaps(DATA_TYPE, DATA_TYPECODE, DIM_TYPE)
</pre>
<p>that can be invoked for appropriate <tt class="docutils literal"><span class="pre">(DATA_TYPE,</span> <span class="pre">DATA_TYPECODE,</span>
<span class="pre">DIM_TYPE)</span></tt> triplets.  For example:</p>
<pre class="literal-block">
%numpy_typemaps(double, NPY_DOUBLE, int)
%numpy_typemaps(int,    NPY_INT   , int)
</pre>
<p>The <tt class="docutils literal"><span class="pre">numpy.i</span></tt> interface file uses the <tt class="docutils literal"><span class="pre">%numpy_typemaps</span></tt> macro to
implement typemaps for the following C data types and <tt class="docutils literal"><span class="pre">int</span></tt>
dimension types:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">signed</span> <span class="pre">char</span></tt></li>
<li><tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">char</span></tt></li>
<li><tt class="docutils literal"><span class="pre">short</span></tt></li>
<li><tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">short</span></tt></li>
<li><tt class="docutils literal"><span class="pre">int</span></tt></li>
<li><tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">int</span></tt></li>
<li><tt class="docutils literal"><span class="pre">long</span></tt></li>
<li><tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">long</span></tt></li>
<li><tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt></li>
<li><tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">long</span> <span class="pre">long</span></tt></li>
<li><tt class="docutils literal"><span class="pre">float</span></tt></li>
<li><tt class="docutils literal"><span class="pre">double</span></tt></li>
</ul>
</blockquote>
<p>In the following descriptions, we reference a generic <tt class="docutils literal"><span class="pre">DATA_TYPE</span></tt>, which
could be any of the C data types listed above, and <tt class="docutils literal"><span class="pre">DIM_TYPE</span></tt> which
should be one of the many types of integers.</p>
<p>The typemap signatures are largely differentiated on the name given to
the buffer pointer.  Names with <tt class="docutils literal"><span class="pre">FARRAY</span></tt> are for FORTRAN-ordered
arrays, and names with <tt class="docutils literal"><span class="pre">ARRAY</span></tt> are for C-ordered (or 1D arrays).</p>
<div class="section">
<h2><a class="toc-backref" href="#id4" id="input-arrays" name="input-arrays">Input Arrays</a></h2>
<p>Input arrays are defined as arrays of data that are passed into a
routine but are not altered in-place or returned to the user.  The
<a class="reference" href="http://www.python.org">python</a> input array is therefore allowed to be almost any <a class="reference" href="http://www.python.org">python</a>
sequence (such as a list) that can be converted to the requested type
of array.  The input array signatures are</p>
<p>1D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">IN_ARRAY1[ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY1,</span> <span class="pre">int</span> <span class="pre">DIM1</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY1</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>2D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">IN_ARRAY2[ANY][ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY2,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_FARRAY2,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_FARRAY2</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>3D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">IN_ARRAY3[ANY][ANY][ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY3,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_ARRAY3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_FARRAY3,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">IN_FARRAY3</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>The first signature listed, <tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">IN_ARRAY[ANY]</span> <span class="pre">)</span></tt> is for
one-dimensional arrays with hard-coded dimensions.  Likewise,
<tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">IN_ARRAY2[ANY][ANY]</span> <span class="pre">)</span></tt> is for two-dimensional arrays
with hard-coded dimensions, and similarly for three-dimensional.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id5" id="in-place-arrays" name="in-place-arrays">In-Place Arrays</a></h2>
<p>In-place arrays are defined as arrays that are modified in-place.  The
input values may or may not be used, but the values at the time the
function returns are significant.  The provided <a class="reference" href="http://www.python.org">python</a> argument
must therefore be a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array of the required type.  The in-place
signatures are</p>
<p>1D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">INPLACE_ARRAY1[ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY1,</span> <span class="pre">int</span> <span class="pre">DIM1</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY1</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>2D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">INPLACE_ARRAY2[ANY][ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY2,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_FARRAY2,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_FARRAY2</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>3D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">INPLACE_ARRAY3[ANY][ANY][ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY3,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_ARRAY3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_FARRAY3,</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">int</span> <span class="pre">DIM2,</span> <span class="pre">int</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">INPLACE_FARRAY3</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>These typemaps now check to make sure that the <tt class="docutils literal"><span class="pre">INPLACE_ARRAY</span></tt>
arguments use native byte ordering.  If not, an exception is raised.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id6" id="argout-arrays" name="argout-arrays">Argout Arrays</a></h2>
<p>Argout arrays are arrays that appear in the input arguments in C, but
are in fact output arrays.  This pattern occurs often when there is
more than one output variable and the single return argument is
therefore not sufficient.  In <a class="reference" href="http://www.python.org">python</a>, the convential way to return
multiple arguments is to pack them into a sequence (tuple, list, etc.)
and return the sequence.  This is what the argout typemaps do.  If a
wrapped function that uses these argout typemaps has more than one
return argument, they are packed into a tuple or list, depending on
the version of <a class="reference" href="http://www.python.org">python</a>.  The <a class="reference" href="http://www.python.org">python</a> user does not pass these
arrays in, they simply get returned.  For the case where a dimension
is specified, the python user must provide that dimension as an
argument.  The argout signatures are</p>
<p>1D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">ARGOUT_ARRAY1[ANY]</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE*</span> <span class="pre">ARGOUT_ARRAY1,</span> <span class="pre">int</span> <span class="pre">DIM1</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">int</span> <span class="pre">DIM1,</span> <span class="pre">DATA_TYPE*</span> <span class="pre">ARGOUT_ARRAY1</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>2D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">ARGOUT_ARRAY2[ANY][ANY]</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>3D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE</span> <span class="pre">ARGOUT_ARRAY3[ANY][ANY][ANY]</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>These are typically used in situations where in C/C++, you would
allocate a(n) array(s) on the heap, and call the function to fill the
array(s) values.  In <a class="reference" href="http://www.python.org">python</a>, the arrays are allocated for you and
returned as new array objects.</p>
<p>Note that we support <tt class="docutils literal"><span class="pre">DATA_TYPE*</span></tt> argout typemaps in 1D, but not 2D
or 3D.  This is because of a quirk with the <a class="reference" href="http://www.swig.org">SWIG</a> typemap syntax and
cannot be avoided.  Note that for these types of 1D typemaps, the
<a class="reference" href="http://www.python.org">python</a> function will take a single argument representing <tt class="docutils literal"><span class="pre">DIM1</span></tt>.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id7" id="argoutview-arrays" name="argoutview-arrays">Argoutview Arrays</a></h2>
<p>Argoutview arrays are for when your C code provides you with a view of
its internal data and does not require any memory to be allocated by
the user.  This can be dangerous.  There is almost no way to guarantee
that the internal data from the C code will remain in existence for
the entire lifetime of the <a class="reference" href="http://numpy.scipy.org">NumPy</a> array that encapsulates it.  If
the user destroys the object that provides the view of the data before
destroying the <a class="reference" href="http://numpy.scipy.org">NumPy</a> array, then using that array my result in bad
memory references or segmentation faults.  Nevertheless, there are
situations, working with large data sets, where you simply have no
other choice.</p>
<p>The C code to be wrapped for argoutview arrays are characterized by
pointers: pointers to the dimensions and double pointers to the data,
so that these values can be passed back to the user.  The argoutview
typemap signatures are therefore</p>
<p>1D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY1</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>2D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_FARRAY2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2</span> <span class="pre">)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_FARRAY2</span> <span class="pre">)</span></tt></li>
</ul>
</blockquote>
<p>3D:</p>
<blockquote>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY3,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM3)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_ARRAY3)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_FARRAY3,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM3)</span></tt></li>
<li><tt class="docutils literal"><span class="pre">(</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM1,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM2,</span> <span class="pre">DIM_TYPE*</span> <span class="pre">DIM3,</span> <span class="pre">DATA_TYPE**</span> <span class="pre">ARGOUTVIEW_FARRAY3)</span></tt></li>
</ul>
</blockquote>
<p>Note that arrays with hard-coded dimensions are not supported.  These
cannot follow the double pointer signatures of these typemaps.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id8" id="output-arrays" name="output-arrays">Output Arrays</a></h2>
<p>The <tt class="docutils literal"><span class="pre">numpy.i</span></tt> interface file does not support typemaps for output
arrays, for several reasons.  First, C/C++ return arguments are
limited to a single value.  This prevents obtaining dimension
information in a general way.  Second, arrays with hard-coded lengths
are not permitted as return arguments.  In other words:</p>
<pre class="literal-block">
double[3] newVector(double x, double y, double z);
</pre>
<p>is not legal C/C++ syntax.  Therefore, we cannot provide typemaps of
the form:</p>
<pre class="literal-block">
%typemap(out) (TYPE[ANY]);
</pre>
<p>If you run into a situation where a function or method is returning a
pointer to an array, your best bet is to write your own version of the
function to be wrapped, either with <tt class="docutils literal"><span class="pre">%extend</span></tt> for the case of class
methods or <tt class="docutils literal"><span class="pre">%ignore</span></tt> and <tt class="docutils literal"><span class="pre">%rename</span></tt> for the case of functions.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id9" id="other-common-types-bool" name="other-common-types-bool">Other Common Types: bool</a></h2>
<p>Note that C++ type <tt class="docutils literal"><span class="pre">bool</span></tt> is not supported in the list in the
<a class="reference" href="#available-typemaps">Available Typemaps</a> section.  NumPy bools are a single byte, while
the C++ <tt class="docutils literal"><span class="pre">bool</span></tt> is four bytes (at least on my system).  Therefore:</p>
<pre class="literal-block">
%numpy_typemaps(bool, NPY_BOOL, int)
</pre>
<p>will result in typemaps that will produce code that reference
improper data lengths.  You can implement the following macro
expansion:</p>
<pre class="literal-block">
%numpy_typemaps(bool, NPY_UINT, int)
</pre>
<p>to fix the data length problem, and <a class="reference" href="#input-arrays">Input Arrays</a> will work fine,
but <a class="reference" href="#in-place-arrays">In-Place Arrays</a> might fail type-checking.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id10" id="other-common-types-complex" name="other-common-types-complex">Other Common Types: complex</a></h2>
<p>Typemap conversions for complex floating-point types is also not
supported automatically.  This is because <a class="reference" href="http://www.python.org">python</a> and <a class="reference" href="http://numpy.scipy.org">NumPy</a> are
written in C, which does not have native complex types.  Both
<a class="reference" href="http://www.python.org">python</a> and <a class="reference" href="http://numpy.scipy.org">NumPy</a> implement their own (essentially equivalent)
<tt class="docutils literal"><span class="pre">struct</span></tt> definitions for complex variables:</p>
<pre class="literal-block">
/* Python */
typedef struct {double real; double imag;} Py_complex;

/* NumPy */
typedef struct {float  real, imag;} npy_cfloat;
typedef struct {double real, imag;} npy_cdouble;
</pre>
<p>We could have implemented:</p>
<pre class="literal-block">
%numpy_typemaps(Py_complex , NPY_CDOUBLE, int)
%numpy_typemaps(npy_cfloat , NPY_CFLOAT , int)
%numpy_typemaps(npy_cdouble, NPY_CDOUBLE, int)
</pre>
<p>which would have provided automatic type conversions for arrays of
type <tt class="docutils literal"><span class="pre">Py_complex</span></tt>, <tt class="docutils literal"><span class="pre">npy_cfloat</span></tt> and <tt class="docutils literal"><span class="pre">npy_cdouble</span></tt>.  However, it
seemed unlikely that there would be any independent (non-<a class="reference" href="http://www.python.org">python</a>,
non-<a class="reference" href="http://numpy.scipy.org">NumPy</a>) application code that people would be using <a class="reference" href="http://www.swig.org">SWIG</a> to
generate a <a class="reference" href="http://www.python.org">python</a> interface to, that also used these definitions
for complex types.  More likely, these application codes will define
their own complex types, or in the case of C++, use <tt class="docutils literal"><span class="pre">std::complex</span></tt>.
Assuming these data structures are compatible with <a class="reference" href="http://www.python.org">python</a> and
<a class="reference" href="http://numpy.scipy.org">NumPy</a> complex types, <tt class="docutils literal"><span class="pre">%numpy_typemap</span></tt> expansions as above (with
the user's complex type substituted for the first argument) should
work.</p>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id11" id="numpy-array-scalars-and-swig" name="numpy-array-scalars-and-swig">NumPy Array Scalars and SWIG</a></h1>
<p><a class="reference" href="http://www.swig.org">SWIG</a> has sophisticated type checking for numerical types.  For
example, if your C/C++ routine expects an integer as input, the code
generated by <a class="reference" href="http://www.swig.org">SWIG</a> will check for both <a class="reference" href="http://www.python.org">python</a> integers and
<a class="reference" href="http://www.python.org">python</a> long integers, and raise an overflow error if the provided
<a class="reference" href="http://www.python.org">python</a> integer is too big to cast down to a C integer.  With the
introduction of <a class="reference" href="http://numpy.scipy.org">NumPy</a> scalar arrays into your <a class="reference" href="http://www.python.org">python</a> code, you
might conceivably extract an integer from a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array and attempt
to pass this to a <a class="reference" href="http://www.swig.org">SWIG</a>-wrapped C/C++ function that expects an
<tt class="docutils literal"><span class="pre">int</span></tt>, but the <a class="reference" href="http://www.swig.org">SWIG</a> type checking will not recognize the <a class="reference" href="http://numpy.scipy.org">NumPy</a>
array scalar as an integer.  (Often, this does in fact work -- it
depends on whether <a class="reference" href="http://numpy.scipy.org">NumPy</a> recognizes the integer type you are using
as inheriting from the <a class="reference" href="http://www.python.org">python</a> integer type on the platform you are
using.  Sometimes, this means that code that works on a 32-bit machine
will fail on a 64-bit machine.)</p>
<p>If you get a <a class="reference" href="http://www.python.org">python</a> error that looks like the following:</p>
<pre class="literal-block">
TypeError: in method 'MyClass_MyMethod', argument 2 of type 'int'
</pre>
<p>and the argument you are passing is an integer extracted from a
<a class="reference" href="http://numpy.scipy.org">NumPy</a> array, then you have stumbled upon this problem.  The
solution is to modify the <a class="reference" href="http://www.swig.org">SWIG</a> type conversion system to accept
<a class="reference" href="http://numpy.scipy.org">Numpy</a> array scalars in addition to the standard integer types.
Fortunately, this capabilitiy has been provided for you.  Simply copy
the file:</p>
<pre class="literal-block">
pyfragments.swg
</pre>
<p>to the working build directory for you project, and this problem will
be fixed.  It is suggested that you do this anyway, as it only
increases the capabilities of your <a class="reference" href="http://www.python.org">python</a> interface.</p>
<div class="section">
<h2><a class="toc-backref" href="#id12" id="why-is-there-a-second-file" name="why-is-there-a-second-file">Why is There a Second File?</a></h2>
<p>The <a class="reference" href="http://www.swig.org">SWIG</a> type checking and conversion system is a complicated
combination of C macros, <a class="reference" href="http://www.swig.org">SWIG</a> macros, <a class="reference" href="http://www.swig.org">SWIG</a> typemaps and <a class="reference" href="http://www.swig.org">SWIG</a>
fragments.  Fragments are a way to conditionally insert code into your
wrapper file if it is needed, and not insert it if not needed.  If
multiple typemaps require the same fragment, the fragment only gets
inserted into your wrapper code once.</p>
<p>There is a fragment for converting a <a class="reference" href="http://www.python.org">python</a> integer to a C
<tt class="docutils literal"><span class="pre">long</span></tt>.  There is a different fragment that converts a <a class="reference" href="http://www.python.org">python</a>
integer to a C <tt class="docutils literal"><span class="pre">int</span></tt>, that calls the rountine defined in the
<tt class="docutils literal"><span class="pre">long</span></tt> fragment.  We can make the changes we want here by changing
the definition for the <tt class="docutils literal"><span class="pre">long</span></tt> fragment.  <a class="reference" href="http://www.swig.org">SWIG</a> determines the
active definition for a fragment using a &quot;first come, first served&quot;
system.  That is, we need to define the fragment for <tt class="docutils literal"><span class="pre">long</span></tt>
conversions prior to <a class="reference" href="http://www.swig.org">SWIG</a> doing it internally.  <a class="reference" href="http://www.swig.org">SWIG</a> allows us
to do this by putting our fragment definitions in the file
<tt class="docutils literal"><span class="pre">pyfragments.swg</span></tt>.  If we were to put the new fragment definitions
in <tt class="docutils literal"><span class="pre">numpy.i</span></tt>, they would be ignored.</p>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id13" id="helper-functions" name="helper-functions">Helper Functions</a></h1>
<p>The <tt class="docutils literal"><span class="pre">numpy.i</span></tt> file containes several macros and routines that it
uses internally to build its typemaps.  However, these functions may
be useful elsewhere in your interface file.  These macros and routines
are implemented as fragments, which are described briefly in the
previous section.  If you try to use one or more of the following
macros or functions, but your compiler complains that it does not
recognize the symbol, then you need to force these fragments to appear
in your code using:</p>
<pre class="literal-block">
%fragment(&quot;NumPy_Fragments&quot;);
</pre>
<p>in your <a class="reference" href="http://www.swig.org">SWIG</a> interface file.</p>
<div class="section">
<h2><a class="toc-backref" href="#id14" id="macros" name="macros">Macros</a></h2>
<blockquote>
<dl class="docutils">
<dt><strong>is_array(a)</strong></dt>
<dd>Evaluates as true if <tt class="docutils literal"><span class="pre">a</span></tt> is non-<tt class="docutils literal"><span class="pre">NULL</span></tt> and can be cast to a
<tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_type(a)</strong></dt>
<dd>Evaluates to the integer data type code of <tt class="docutils literal"><span class="pre">a</span></tt>, assuming <tt class="docutils literal"><span class="pre">a</span></tt> can
be cast to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_numdims(a)</strong></dt>
<dd>Evaluates to the integer number of dimensions of <tt class="docutils literal"><span class="pre">a</span></tt>, assuming
<tt class="docutils literal"><span class="pre">a</span></tt> can be cast to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_dimensions(a)</strong></dt>
<dd>Evaluates to an array of type <tt class="docutils literal"><span class="pre">npy_intp</span></tt> and length
<tt class="docutils literal"><span class="pre">array_numdims(a)</span></tt>, giving the lengths of all of the dimensions
of <tt class="docutils literal"><span class="pre">a</span></tt>, assuming <tt class="docutils literal"><span class="pre">a</span></tt> can be cast to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_size(a,i)</strong></dt>
<dd>Evaluates to the <tt class="docutils literal"><span class="pre">i</span></tt>-th dimension size of <tt class="docutils literal"><span class="pre">a</span></tt>, assuming <tt class="docutils literal"><span class="pre">a</span></tt>
can be cast to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_data(a)</strong></dt>
<dd>Evaluates to a pointer of type <tt class="docutils literal"><span class="pre">void*</span></tt> that points to the data
buffer of <tt class="docutils literal"><span class="pre">a</span></tt>, assuming <tt class="docutils literal"><span class="pre">a</span></tt> can be cast to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>.</dd>
<dt><strong>array_is_contiguous(a)</strong></dt>
<dd>Evaluates as true if <tt class="docutils literal"><span class="pre">a</span></tt> is a contiguous array.  Equivalent to
<tt class="docutils literal"><span class="pre">(PyArray_ISCONTIGUOUS(a))</span></tt>.</dd>
<dt><strong>array_is_native(a)</strong></dt>
<dd>Evaluates as true if the data buffer of <tt class="docutils literal"><span class="pre">a</span></tt> uses native byte
order.  Equivalent to <tt class="docutils literal"><span class="pre">(PyArray_ISNOTSWAPPED(a))</span></tt>.</dd>
<dt><strong>array_is_fortran(a)</strong></dt>
<dd>Evaluates as true if <tt class="docutils literal"><span class="pre">a</span></tt> is FORTRAN ordered.</dd>
</dl>
</blockquote>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id15" id="routines" name="routines">Routines</a></h2>
<blockquote>
<p><strong>pytype_string()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">char*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyObject*</span> <span class="pre">py_obj</span></tt>, a general <a class="reference" href="http://www.python.org">python</a> object.</li>
</ul>
<p>Return a string describing the type of <tt class="docutils literal"><span class="pre">py_obj</span></tt>.</p>
</blockquote>
<p><strong>typecode_string()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">char*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">typecode</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> integer typecode.</li>
</ul>
<p>Return a string describing the type corresponding to the <a class="reference" href="http://numpy.scipy.org">NumPy</a>
<tt class="docutils literal"><span class="pre">typecode</span></tt>.</p>
</blockquote>
<p><strong>type_match()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">actual_type</span></tt>, the <a class="reference" href="http://numpy.scipy.org">NumPy</a> typecode of a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">desired_type</span></tt>, the desired <a class="reference" href="http://numpy.scipy.org">NumPy</a> typecode.</li>
</ul>
<p>Make sure that <tt class="docutils literal"><span class="pre">actual_type</span></tt> is compatible with
<tt class="docutils literal"><span class="pre">desired_type</span></tt>.  For example, this allows character and
byte types, or int and long types, to match.  This is now
equivalent to <tt class="docutils literal"><span class="pre">PyArray_EquivTypenums()</span></tt>.</p>
</blockquote>
<p><strong>obj_to_array_no_conversion()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyObject*</span> <span class="pre">input</span></tt>, a general <a class="reference" href="http://www.python.org">python</a> object.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">typecode</span></tt>, the desired <a class="reference" href="http://numpy.scipy.org">NumPy</a> typecode.</li>
</ul>
<p>Cast <tt class="docutils literal"><span class="pre">input</span></tt> to a <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt> if legal, and ensure that
it is of type <tt class="docutils literal"><span class="pre">typecode</span></tt>.  If <tt class="docutils literal"><span class="pre">input</span></tt> cannot be cast, or the
<tt class="docutils literal"><span class="pre">typecode</span></tt> is wrong, set a <a class="reference" href="http://www.python.org">python</a> error and return <tt class="docutils literal"><span class="pre">NULL</span></tt>.</p>
</blockquote>
<p><strong>obj_to_array_allow_conversion()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyObject*</span> <span class="pre">input</span></tt>, a general <a class="reference" href="http://www.python.org">python</a> object.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">typecode</span></tt>, the desired <a class="reference" href="http://numpy.scipy.org">NumPy</a> typecode of the resulting
array.</li>
<li><tt class="docutils literal"><span class="pre">int*</span> <span class="pre">is_new_object</span></tt>, returns a value of 0 if no conversion
performed, else 1.</li>
</ul>
<p>Convert <tt class="docutils literal"><span class="pre">input</span></tt> to a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array with the given <tt class="docutils literal"><span class="pre">typecode</span></tt>.
On success, return a valid <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt> with the correct
type.  On failure, the <a class="reference" href="http://www.python.org">python</a> error string will be set and the
routine returns <tt class="docutils literal"><span class="pre">NULL</span></tt>.</p>
</blockquote>
<p><strong>make_contiguous()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
<li><tt class="docutils literal"><span class="pre">int*</span> <span class="pre">is_new_object</span></tt>, returns a value of 0 if no conversion
performed, else 1.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">min_dims</span></tt>, minimum allowable dimensions.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">max_dims</span></tt>, maximum allowable dimensions.</li>
</ul>
<p>Check to see if <tt class="docutils literal"><span class="pre">ary</span></tt> is contiguous.  If so, return the input
pointer and flag it as not a new object.  If it is not contiguous,
create a new <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt> using the original data, flag it
as a new object and return the pointer.</p>
</blockquote>
<p><strong>obj_to_array_contiguous_allow_conversion()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyObject*</span> <span class="pre">input</span></tt>, a general <a class="reference" href="http://www.python.org">python</a> object.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">typecode</span></tt>, the desired <a class="reference" href="http://numpy.scipy.org">NumPy</a> typecode of the resulting
array.</li>
<li><tt class="docutils literal"><span class="pre">int*</span> <span class="pre">is_new_object</span></tt>, returns a value of 0 if no conversion
performed, else 1.</li>
</ul>
<p>Convert <tt class="docutils literal"><span class="pre">input</span></tt> to a contiguous <tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt> of the
specified type.  If the input object is not a contiguous
<tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>, a new one will be created and the new object
flag will be set.</p>
</blockquote>
<p><strong>require_contiguous()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
</ul>
<p>Test whether <tt class="docutils literal"><span class="pre">ary</span></tt> is contiguous.  If so, return 1.  Otherwise,
set a <a class="reference" href="http://www.python.org">python</a> error and return 0.</p>
</blockquote>
<p><strong>require_native()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArray_Object*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
</ul>
<p>Require that <tt class="docutils literal"><span class="pre">ary</span></tt> is not byte-swapped.  If the array is not
byte-swapped, return 1.  Otherwise, set a <a class="reference" href="http://www.python.org">python</a> error and
return 0.</p>
</blockquote>
<p><strong>require_dimensions()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">exact_dimensions</span></tt>, the desired number of dimensions.</li>
</ul>
<p>Require <tt class="docutils literal"><span class="pre">ary</span></tt> to have a specified number of dimensions.  If the
array has the specified number of dimensions, return 1.
Otherwise, set a <a class="reference" href="http://www.python.org">python</a> error and return 0.</p>
</blockquote>
<p><strong>require_dimensions_n()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
<li><tt class="docutils literal"><span class="pre">int*</span> <span class="pre">exact_dimensions</span></tt>, an array of integers representing
acceptable numbers of dimensions.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">n</span></tt>, the length of <tt class="docutils literal"><span class="pre">exact_dimensions</span></tt>.</li>
</ul>
<p>Require <tt class="docutils literal"><span class="pre">ary</span></tt> to have one of a list of specified number of
dimensions.  If the array has one of the specified number of
dimensions, return 1.  Otherwise, set the <a class="reference" href="http://www.python.org">python</a> error string
and return 0.</p>
</blockquote>
<p><strong>require_size()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
<li><tt class="docutils literal"><span class="pre">npy_int*</span> <span class="pre">size</span></tt>, an array representing the desired lengths of
each dimension.</li>
<li><tt class="docutils literal"><span class="pre">int</span> <span class="pre">n</span></tt>, the length of <tt class="docutils literal"><span class="pre">size</span></tt>.</li>
</ul>
<p>Require <tt class="docutils literal"><span class="pre">ary</span></tt> to have a specified shape.  If the array has the
specified shape, return 1.  Otherwise, set the <a class="reference" href="http://www.python.org">python</a> error
string and return 0.</p>
</blockquote>
<p><strong>require_fortran()</strong></p>
<blockquote>
<p>Return type: <tt class="docutils literal"><span class="pre">int</span></tt></p>
<p>Arguments:</p>
<ul class="simple">
<li><tt class="docutils literal"><span class="pre">PyArrayObject*</span> <span class="pre">ary</span></tt>, a <a class="reference" href="http://numpy.scipy.org">NumPy</a> array.</li>
</ul>
<p>Require the given <tt class="docutils literal"><span class="pre">PyArrayObject</span></tt> to to be FORTRAN ordered.  If
the the <tt class="docutils literal"><span class="pre">PyArrayObject</span></tt> is already FORTRAN ordered, do nothing.
Else, set the FORTRAN ordering flag and recompute the strides.</p>
</blockquote>
</blockquote>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id16" id="beyond-the-provided-typemaps" name="beyond-the-provided-typemaps">Beyond the Provided Typemaps</a></h1>
<p>There are many C or C++ array/<a class="reference" href="http://numpy.scipy.org">NumPy</a> array situations not covered by
a simple <tt class="docutils literal"><span class="pre">%include</span> <span class="pre">&quot;numpy.i&quot;</span></tt> and subsequent <tt class="docutils literal"><span class="pre">%apply</span></tt> directives.</p>
<div class="section">
<h2><a class="toc-backref" href="#id17" id="a-common-example" name="a-common-example">A Common Example</a></h2>
<p>Consider a reasonable prototype for a dot product function:</p>
<pre class="literal-block">
double dot(int len, double* vec1, double* vec2);
</pre>
<p>The <a class="reference" href="http://www.python.org">python</a> interface that we want is:</p>
<pre class="literal-block">
def dot(vec1, vec2):
    &quot;&quot;&quot;
    dot(PyObject,PyObject) -&gt; double
    &quot;&quot;&quot;
</pre>
<p>The problem here is that there is one dimension argument and two array
arguments, and our typemaps are set up for dimensions that apply to a
single array (in fact, <a class="reference" href="http://www.swig.org">SWIG</a> does not provide a mechanism for
associating <tt class="docutils literal"><span class="pre">len</span></tt> with <tt class="docutils literal"><span class="pre">vec2</span></tt> that takes two <a class="reference" href="http://www.python.org">python</a> input
arguments).  The recommended solution is the following:</p>
<pre class="literal-block">
%apply (int DIM1, double* IN_ARRAY1) {(int len1, double* vec1),
                                      (int len2, double* vec2)}
%rename (dot) my_dot;
%exception my_dot {
    $action
    if (PyErr_Occurred()) SWIG_fail;
}
%inline %{
double my_dot(int len1, double* vec1, int len2, double* vec2) {
    if (len1 != len2) {
        PyErr_Format(PyExc_ValueError,
                     &quot;Arrays of lengths (%d,%d) given&quot;,
                     len1, len2);
        return 0.0;
    }
    return dot(len1, vec1, vec2);
}
%}
</pre>
<p>If the header file that contains the prototype for <tt class="docutils literal"><span class="pre">double</span> <span class="pre">dot()</span></tt>
also contains other prototypes that you want to wrap, so that you need
to <tt class="docutils literal"><span class="pre">%include</span></tt> this header file, then you will also need a <tt class="docutils literal"><span class="pre">%ignore</span>
<span class="pre">dot;</span></tt> directive, placed after the <tt class="docutils literal"><span class="pre">%rename</span></tt> and before the
<tt class="docutils literal"><span class="pre">%include</span></tt> directives.  Or, if the function in question is a class
method, you will want to use <tt class="docutils literal"><span class="pre">%extend</span></tt> rather than <tt class="docutils literal"><span class="pre">%inline</span></tt> in
addition to <tt class="docutils literal"><span class="pre">%ignore</span></tt>.</p>
<p><strong>A note on error handling:</strong> Note that <tt class="docutils literal"><span class="pre">my_dot</span></tt> returns a
<tt class="docutils literal"><span class="pre">double</span></tt> but that it can also raise a <a class="reference" href="http://www.python.org">python</a> error.  The
resulting wrapper function will return a <a class="reference" href="http://www.python.org">python</a> float
representation of 0.0 when the vector lengths do not match.  Since
this is not <tt class="docutils literal"><span class="pre">NULL</span></tt>, the <a class="reference" href="http://www.python.org">python</a> interpreter will not know to check
for an error.  For this reason, we add the <tt class="docutils literal"><span class="pre">%exception</span></tt> directive
above for <tt class="docutils literal"><span class="pre">my_dot</span></tt> to get the behavior we want (note that
<tt class="docutils literal"><span class="pre">$action</span></tt> is a macro that gets expanded to a valid call to
<tt class="docutils literal"><span class="pre">my_dot</span></tt>).  In general, you will probably want to write a <a class="reference" href="http://www.swig.org">SWIG</a>
macro to perform this task.</p>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id18" id="other-situations" name="other-situations">Other Situations</a></h2>
<p>There are other wrapping situations in which <tt class="docutils literal"><span class="pre">numpy.i</span></tt> may be
helpful when you encounter them.</p>
<blockquote>
<ul>
<li><p class="first">In some situations, it is possible that you could use the
<tt class="docutils literal"><span class="pre">%numpy_templates</span></tt> macro to implement typemaps for your own
types.  See the <a class="reference" href="#other-common-types-bool">Other Common Types: bool</a> or <a class="reference" href="#other-common-types-complex">Other Common
Types: complex</a> sections for examples.  Another situation is if
your dimensions are of a type other than <tt class="docutils literal"><span class="pre">int</span></tt> (say <tt class="docutils literal"><span class="pre">long</span></tt> for
example):</p>
<pre class="literal-block">
%numpy_typemaps(double, NPY_DOUBLE, long)
</pre>
</li>
<li><p class="first">You can use the code in <tt class="docutils literal"><span class="pre">numpy.i</span></tt> to write your own typemaps.
For example, if you had a four-dimensional array as a function
argument, you could cut-and-paste the appropriate
three-dimensional typemaps into your interface file.  The
modifications for the fourth dimension would be trivial.</p>
</li>
<li><p class="first">Sometimes, the best approach is to use the <tt class="docutils literal"><span class="pre">%extend</span></tt> directive
to define new methods for your classes (or overload existing ones)
that take a <tt class="docutils literal"><span class="pre">PyObject*</span></tt> (that either is or can be converted to a
<tt class="docutils literal"><span class="pre">PyArrayObject*</span></tt>) instead of a pointer to a buffer.  In this
case, the helper routines in <tt class="docutils literal"><span class="pre">numpy.i</span></tt> can be very useful.</p>
</li>
<li><p class="first">Writing typemaps can be a bit nonintuitive.  If you have specific
questions about writing <a class="reference" href="http://www.swig.org">SWIG</a> typemaps for <a class="reference" href="http://numpy.scipy.org">NumPy</a>, the
developers of <tt class="docutils literal"><span class="pre">numpy.i</span></tt> do monitor the
<a class="reference" href="mailto:Numpy-discussion&#64;scipy.org">Numpy-discussion</a> and
<a class="reference" href="mailto:Swig-user&#64;lists.sourceforge.net">Swig-user</a> mail lists.</p>
</li>
</ul>
</blockquote>
</div>
<div class="section">
<h2><a class="toc-backref" href="#id19" id="a-final-note" name="a-final-note">A Final Note</a></h2>
<p>When you use the <tt class="docutils literal"><span class="pre">%apply</span></tt> directive, as is usually necessary to use
<tt class="docutils literal"><span class="pre">numpy.i</span></tt>, it will remain in effect until you tell <a class="reference" href="http://www.swig.org">SWIG</a> that it
shouldn't be.  If the arguments to the functions or methods that you
are wrapping have common names, such as <tt class="docutils literal"><span class="pre">length</span></tt> or <tt class="docutils literal"><span class="pre">vector</span></tt>,
these typemaps may get applied in situations you do not expect or
want.  Therefore, it is always a good idea to add a <tt class="docutils literal"><span class="pre">%clear</span></tt>
directive after you are done with a specific typemap:</p>
<pre class="literal-block">
%apply (double* IN_ARRAY1, int DIM1) {(double* vector, int length)}
%include &quot;my_header.h&quot;
%clear (double* vector, int length);
</pre>
<p>In general, you should target these typemap signatures specifically
where you want them, and then clear them after you are done.</p>
</div>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id20" id="summary" name="summary">Summary</a></h1>
<p>Out of the box, <tt class="docutils literal"><span class="pre">numpy.i</span></tt> provides typemaps that support conversion
between <a class="reference" href="http://numpy.scipy.org">NumPy</a> arrays and C arrays:</p>
<blockquote>
<ul class="simple">
<li>That can be one of 12 different scalar types: <tt class="docutils literal"><span class="pre">signed</span> <span class="pre">char</span></tt>,
<tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">char</span></tt>, <tt class="docutils literal"><span class="pre">short</span></tt>, <tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">short</span></tt>, <tt class="docutils literal"><span class="pre">int</span></tt>,
<tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">int</span></tt>, <tt class="docutils literal"><span class="pre">long</span></tt>, <tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">long</span></tt>, <tt class="docutils literal"><span class="pre">long</span> <span class="pre">long</span></tt>,
<tt class="docutils literal"><span class="pre">unsigned</span> <span class="pre">long</span> <span class="pre">long</span></tt>, <tt class="docutils literal"><span class="pre">float</span></tt> and <tt class="docutils literal"><span class="pre">double</span></tt>.</li>
<li>That support 41 different argument signatures for each data type,
including:<ul>
<li>One-dimensional, two-dimensional and three-dimensional arrays.</li>
<li>Input-only, in-place, argout and argoutview behavior.</li>
<li>Hard-coded dimensions, data-buffer-then-dimensions
specification, and dimensions-then-data-buffer specification.</li>
<li>Both C-ordering (&quot;last dimension fastest&quot;) or FORTRAN-ordering
(&quot;first dimension fastest&quot;) support for 2D and 3D arrays.</li>
</ul>
</li>
</ul>
</blockquote>
<p>The <tt class="docutils literal"><span class="pre">numpy.i</span></tt> interface file also provides additional tools for
wrapper developers, including:</p>
<blockquote>
<ul class="simple">
<li>A <a class="reference" href="http://www.swig.org">SWIG</a> macro (<tt class="docutils literal"><span class="pre">%numpy_typemaps</span></tt>) with three arguments for
implementing the 41 argument signatures for the user's choice of
(1) C data type, (2) <a class="reference" href="http://numpy.scipy.org">NumPy</a> data type (assuming they match), and
(3) dimension type.</li>
<li>Nine C macros and 13 C functions that can be used to write
specialized typemaps, extensions, or inlined functions that handle
cases not covered by the provided typemaps.</li>
</ul>
</blockquote>
</div>
<div class="section">
<h1><a class="toc-backref" href="#id21" id="acknowledgements" name="acknowledgements">Acknowledgements</a></h1>
<p>Many people have worked to glue <a class="reference" href="http://www.swig.org">SWIG</a> and <a class="reference" href="http://numpy.scipy.org">NumPy</a> together (as well
as <a class="reference" href="http://www.swig.org">SWIG</a> and the predecessors of <a class="reference" href="http://numpy.scipy.org">NumPy</a>, Numeric and numarray).
The effort to standardize this work into <tt class="docutils literal"><span class="pre">numpy.i</span></tt> began at the 2005
<a class="reference" href="http://scipy.org">SciPy</a> Conference with a conversation between
Fernando Perez and myself.  Fernando collected helper functions and
typemaps from Eric Jones, Michael Hunter, Anna Omelchenko and Michael
Sanner.  Sebastian Hasse and Georg Holzmann have also provided
additional error checking and use cases.  The work of these
contributors has made this end result possible.</p>
</div>
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